1. Technical Field of the Invention
The present invention relates in general to horticultural and agricultural lighting systems used in developing and growing plants in controlled environments. More specifically, the present invention relates to a horticulture light fixture having an integrated very high output (VHO) fluorescent lamp and ballast.
2. Description of the Related Art
Indoor gardens, green houses, hydroponics systems, and isolated carbon dioxide growing chambers all require light to grow plants. Currently, the most common grow-light source is HID (High Intensity Discharge) lamps constructed from high pressure sodium and metal halide technologies. The HID lamps have been a mainstay in the indoor gardening market for over 20 years, but technology advancements in fluorescent lamps and the ballasts that power the same now produce efficient lumens in adequate quantity to viably grow plants that before only could be grown by HID lamps at much lower power efficiencies.
Attenuation of light is a major issue faced by plant growers around the world. Plant growers prefer to position the light fixture close and above the growing plants in order to limit the effects of attenuation. Attenuation is the gradual loss in intensity of any kind of flux through a medium. For instance, sunlight is attenuated by atmosphere, and X-rays are attenuated by lead. In either example, the “distance” the flux must travel through the medium directly impacts the loss of intensity. Therefore it follows that the greater the distance between the lamp and the plants, the more lumens lost in the atmosphere in between. In short, the user of a grow light fixture desires a location of the fixture as close to the plants as possible, without causing heat impact on the plants that will stunt development, cause curl, or kill the plant.
Heat produced by the light fixture is always a design challenge and concern. The HID lamps by consequence of high lumen output with low power efficiencies produce undesirable amounts of heat. The thermal pollution or heat generated must then be isolated and removed from the growing environment. In order to combat the negative effects of heat, light fixtures with various active cooling systems were developed. These cooling systems rely upon a fan or fans, pushing or pulling isolated cooling atmosphere through the fixture, and the heated atmosphere out of the fixture away from plants. [See U.S. Application 2008/025071 Townsley] The fixture may be placed close to growing plants without worry of plant harm due to excessive temperatures.
Many attempts have been made for manufacturing grow light fixtures adapted for combating the negative effects of heat, while still benefitting from the simplicity of having the ballast integrated within the light fixture. [See U.S. Pat. No. 7,524,090 Hargreaves] Integrating a ballast within the fixture for easy install has been accomplished for HID by force cooling fans, and isolating the ballast with an air gap. Fluorescents up until recently, did not produce the quantity of lumens required to grow plants through the flowing and fruiting phase, leaving HID lamps as the first choice as a yield grow light. Also, the lower lumen output T-5 lamps did not generate enough heat to cause premature failure of the ballast when integrated within the fixture, so passive cooling with vents was enough. The new and recently developed higher lumen output linear T-5 lamps referred to as Very High Output (VHO) creates new design challenges in integrating the ballast within the fixture. The VHO lamps show potential to replace the HID lamps as the standard for the industry.
HID has been the market standard for high lumen output for yielding plants, and the forced air cooling feature is well known in this art. Fluorescents have been a market standard for starting plants or developing plants, leaving the flowering and fruiting yields to the HID. Prior to reaching new levels of lumen output, most fluorescent fixtures were passively cooled, and the ballast for powering the fluorescent lamps were in most applications easily located within the fixture without concern of premature failure due to heat soaking. With the new VHO lamp development, the VHO fluorescent lamps can produce lumens in quantity matching HIDs, at a greater lumen per electrical watt efficiency. This new VHO increase in lumen power, comes substantial heat production increase, and thermal problems when attempting to integrate the ballast within the fixture.
To further compound the issue, the power requirements of the VHO lamp is more than the old fluorescent T-5 lamp, thereby requiring more power from the ballast, thereby increasing the heat generated by the ballast. The increase lamp temperatures coupled with the increased ballast temperatures require a fan or forced air cooling system to remove the excess heat. But just removing the heat is not enough, the fluorescent lamps benefit from a cooled center section, while further benefitting from warmer lamp ends. In short, the fixture must be forced air cooled, each lamp cooled in the middle, kept heated on the ends, the heat sealed from the growing environment while maintaining the ballast within operating temperatures.
Fluorescent lamps, especially the smaller T-5 tubes such as the VHO lamps, require optimum temperatures in order to produce maximum lumens, and operate at maximum life expectancy. Lumen output depends on two variable temperatures, a first temperature immediately around the body of the linear lamp, and a “cold” spot temperature of the lamp at the electrodes or ends. A first temperature around 95 degrees Fahrenheit maximizes lumen production of the T-5 bulb. However, the ends or cold spots located around the electrode require a higher temperature, around 110 to 115 degrees Fahrenheit for maximum performance. Not only do the lamps need to be cooled in the middle, along body of the lamp, but the ends or electrodes require increased temperatures in order to perform optimally.
Some other light fixtures utilize simple methods to raise the temperature of the cold spots on fluorescent bulbs involving cylindrical sleeves attached around the ends or electrodes covering the cold spots. [See U.S. Patent Application 2006/0055293 Ngai] The method of sleeving or insulating the lamp ends require additional hardware and maintenance. Each time a lamp is replaced, a sleeve must be installed increasing expense and complexity.
The new VHO lamps require a fixture able to maximize performance of the lamps by regulating their temperature, while preventing premature thermal failure of the ballast.